Question

我使用python / cython开发了一个实用程序来对CSV文件进行排序并为客户端生成统计信息，但是在我的映射函数有机会执行之前调用pool.map似乎会引发异常。排序少量文件似乎按预期运行，但随着文件数量增加到10，我在调用pool.map后得到以下IndexError。有没有人碰巧认出以下错误？非常感谢任何帮助。

虽然代码在NDA下，但用例非常简单：

代码示例：

def sort_files(csv_files):
    pool_size = multiprocessing.cpu_count()
    pool = multiprocessing.Pool(processes=pool_size)
    sorted_dicts = pool.map(sort_file, csv_files, 1)
    return sorted_dicts

def sort_file(csv_file):
    print 'sorting %s...' % csv_file
    # sort code

输出：

File "generic.pyx", line 17, in generic.sort_files (/users/cyounker/.pyxbld/temp.linux-x86_64-2.7/pyrex/generic.c:1723)
    sorted_dicts = pool.map(sort_file, csv_files, 1)
  File "/usr/lib64/python2.7/multiprocessing/pool.py", line 227, in map
    return self.map_async(func, iterable, chunksize).get()
  File "/usr/lib64/python2.7/multiprocessing/pool.py", line 528, in get
    raise self._value
IndexError: list index out of range

Answer 1

IndexError是你在sort_file（）中的某个地方出现的错误，即在子进程中。它由父进程重新引发。显然multiprocessing没有试图告诉我们错误的真正来源（例如，它出现在哪一行上），甚至没有告诉我们sort_file（）的哪个参数引起它。我更讨厌multiprocessing： - （

Answer 2

在命令输出中进一步检查。至少在Python 3.4中，multiprocessing.pool将有助于在父进程回溯之上打印RemoteTraceback。你会看到类似的东西：

multiprocessing.pool.RemoteTraceback: 
"""
Traceback (most recent call last):
  File "/usr/lib/python3.4/multiprocessing/pool.py", line 119, in worker
    result = (True, func(*args, **kwds))
  File "/usr/lib/python3.4/multiprocessing/pool.py", line 44, in mapstar
    return list(map(*args))
  File "/path/to/your/code/here.py", line 80, in sort_file
    something = row[index]
IndexError: list index out of range
"""

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "generic.pyx", line 17, in generic.sort_files (/users/cyounker/.pyxbld/temp.linux-x86_64-2.7/pyrex/generic.c:1723)
    sorted_dicts = pool.map(sort_file, csv_files, 1)
  File "/usr/lib64/python2.7/multiprocessing/pool.py", line 227, in map
    return self.map_async(func, iterable, chunksize).get()
  File "/usr/lib64/python2.7/multiprocessing/pool.py", line 528, in get
    raise self._value
IndexError: list index out of range

在上述情况中，引发错误的代码位于/path/to/your/code/here.py", line 80

另见debugging errors in python multiprocessing

Python多处理pool.map引发IndexError

2 个答案: